JP3342437B2 - Information recording method for optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recording information on an optical recording medium.

[0002]

2. Description of the Related Art Recently, a write-once disc using an organic dye material for a recording layer has been studied. FIG. 1 shows the basic structure of this kind of disc. In the figure, (1) is a transparent substrate, (2) is a dye layer, (3) is a reflective layer, and (4)
Is a protective layer. Writing of information is performed by converging a high-level laser beam on the dye layer (2). FIG. 2 is a diagram showing a cross section of the disc when information is written. As shown in the drawing, after writing information, a pit (5) is formed in the dye layer (2). Such a pit is formed in a spiral shape, for example, like an existing compact disk (CD), and information is held with the length of the pits and the length between the pits.

[0003] This type of disc is introduced, for example, in Nikkei Electronics, January 23, 1989, p107. According to the document, there is a disclosure that the reflectance of the pit portion decreases because the thickness of the recording layer in the pit portion is smaller than that in the unrecorded portion. It is also disclosed that this decrease in reflectance occurs based on the phase difference of light. or,
It is disclosed that the reflectance of an unrecorded portion can be set to 78%, and that the refractive index of the dye material and the thickness of the dye layer are set to optimum values in advance in order to realize such a high reflectance.

[0004]

However, the above document does not disclose a specific structure of the disk, such as the thickness of the dye layer. Actually, there should be an optimum value for the optical constant of the disk material, the disk size, and the like so that the disk can be recorded and reproduced well.

Accordingly, the present invention provides a method for recording information on an optical recording medium that enables good recording and reproduction.

[0006]

An information recording method for an optical recording medium according to the present invention comprises: a transparent substrate made of polycarbonate;
Recording laser beam on an optical recording medium comprising a light-transmitting recording layer formed on the transparent substrate, and a reflective layer formed on the recording layer and made of gold, silver, copper or an alloy thereof. To reduce the thickness of the recording portion of the recording layer
A method for recording information by reducing the reflectivity of the recording layer by Rukoto, the intensity of the recording laser beam, the thickness of the recording portion of the recording layer is set to be d _1, the The optical recording medium is irradiated with a set recording laser beam. Where d ₁ is n ₀ , the refractive index of the transparent substrate is n ₀ , the real component of the complex refractive index of the recording layer, the imaginary component is n ₁ , k ₁ , the real component of the complex refractive index of the reflective layer, and the imaginary component is n ₂ , k ₂ , when the wavelength of the laser beam is λ,

(Equation 2) (M is an integer where d ₁ is positive and the reflectance at the interface between the transparent substrate and the recording layer is minimal at d ₁ ).
Further, in the information recording method for an optical recording medium according to the present invention, in the above formula for determining the thickness d ₁ of a recording portion of the recording layer, m
Is set such that the intensity of the recording laser beam is minimized.

[0007]

[0008]

[0009]

[0010]

[0011]

For example, three kinds of materials having different refractive indexes are shown in FIG.
When they are superimposed as described above, a reflective surface is formed at the interface between the respective materials. Now, from the first material (100) to the second material (20)
When the beam (B) is incident toward 0), a part of the beam is reflected by the interface (first interface) (101), and the rest is transmitted through the interface (101). In addition, the transmitted beam is applied to a second material (200).
(Second interface) between the second material and the third material (300) (2
01) is similarly reflected and transmitted. Among them, the beam reflected by the second interface (201) is transmitted and reflected at the further first interface (101). Therefore, from the first interface (101), the beam (B1) reflected by the interface in the direction of the first material (100) and the second material (200) from the first interface (10).
A beam obtained by combining the beam (B2) transmitted through 1) is obtained. Here, the beam transmitted from the second material (200) to the first interface (101) includes a beam transmitted through the interface after being reflected plural times by each of the interfaces. Therefore, in this case, the reflectance of the first interface is
It is necessary to focus on not only the beam reflected by the first interface but also the beam transmitted through the first interface.

Such a reflectance is called an amplitude reflectance, and it is generally known that the reflectance is represented by Equation 3 as disclosed in “Thin Film”, page 197, published by Shokabo.

[0014]

(Equation 3)

Here, r ₁ is the reflectance of the first interface (101) viewed from the first material (100), and r ₂ is the reflection of the second interface (201) viewed from the second material (200). Rate. Also, δ is when the beam is perpendicularly incident on each interface,
It is represented by Equation 4.

[0016]

(Equation 4)

Here, λ is the wavelength of the beam, and n and d are the second
Is the refractive index and thickness of the material. As can be seen from Equations 3 and 4, in this case, the amplitude reflectance of the first interface is
It depends on the thickness of the second material. In the case of the present invention, the first material corresponds to a transparent substrate, the second material corresponds to a recording layer, and the third material corresponds to a reflective layer.

The refractive index of the transparent substrate is n ₀ , the real and imaginary components of the complex refractive index of the recording layer are n ₁ and k ₁ , and the complex refractive index of the reflection layer is n ₁ and k ₁ .
It is known that the first and second interface reflectivities r ₁ and r ₂ can be obtained by Equations 5 and 6 where n ₂ and k ₂ are the real and imaginary components of the folding factor.

[0019]

(Equation 5)

[0020]

(Equation 6)

Here, | r ₁ |, | r ₂ |, δ ₁ , and δ ₂ are represented by Expressions 7, 8, 9, and 10.

[0022]

(Equation 7)

[0023]

(Equation 8)

[0024]

(Equation 9)

[0025]

(Equation 10)

However, when the beam passes through the recording layer,
This beam undergoes a phase change and amplitude attenuation. Therefore, it is necessary to determine the amplitude reflectance of the second interface in consideration of the phase change and the amplitude attenuation corresponding to the thickness of the recording layer. When Equation 6 is changed in consideration of such a point, Equations 11 and 12 are obtained as the amplitude reflectance r ₂ of the second interface.

[0027]

[Equation 11]

[0028]

(Equation 12)

As described above, when Equations 3 to 12 are put together, the amplitude reflectance of the first interface is expressed as Equation 13.

[0030]

(Equation 13)

Since it is known that the reflectance of the first interface is equivalent to the square of the amplitude reflectance, the reflectance of the first interface is finally obtained by Expression 14.

[0032]

[Equation 14]

The reflectivity R represented by the equation (14) is expressed by a film thickness d
Changes periodically, as shown in the graph of FIG.

[0034]

(Equation 15)

At this point, the minimum or maximum is reached,

[0036]

(Equation 16)

At this point, the maximum or minimum is reached.

[0038]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described.
explain. In this embodiment, n₁= 4.5, k₁Optical constant of = 0.2
A cyanine dye having a complex number (complex refractive index)
N ₀= Formed on 1.5 polycarbonate substrate
And furthermore, n_Two= 0.17, k_TwoOptical constant of = 4.84
Copper with a thickness of 1000mm by vacuum evaporation
Then, a disk having the structure shown in FIG. 1 is manufactured.

For the disk manufactured in this way,
An experiment was conducted in which the thickness of the dye layer was variously changed, and the reflectance of the disk at this time was measured. The wavelength of the laser beam used in the experiment is λ = 0.78 μm. FIG. 4 shows the measurement results of the reflectance by this experiment.

[0040] The logical expression with the graph shown in FIG. (Number 1
When compared with the graph according to 4) (FIG. 3), they are similar in waveform. According to the graph of FIG. 4 showing the measurement results, the thicknesses of the dye layers corresponding to the maximum value and the minimum value of the reflectance are 720 ° and 260 °, respectively. When the thicknesses of the dye layers corresponding to the maximum value and the minimum value of the reflectance are calculated from Expressions (15) and (16), the thicknesses are 750 ° and 320 °, respectively, and the calculated values substantially match the measured values. Therefore, the characteristic of the change in the disk reflectivity according to the change in the thickness of the dye layer is represented by the logical expression
It has been confirmed that approximation can be made by (Equation 14) .

Next, a disc having a recording layer thickness near the maximum value obtained by the above measurement was applied to a disc having the same wavelength (λ
(0.78 μm) and laser beams having different intensity levels were irradiated to the spot diameter of 2 μm for 500 nsec, and an experiment was performed to measure the change in the reflectance of the disk at this time. FIG. 5 shows the measurement results of the same experiment.

In the same experiment, it is assumed that the melting of the dye layer proceeds as the intensity of the laser beam increases, and therefore, the optical thickness of the dye layer decreases. According to the previous experiment, when the thickness of the dye layer is reduced from 720 mm, the reflectivity of the disk tends to be minimum after around 260 mm and then gradually increase. Which corresponds to the characteristic of FIG. Further, the minimum value of the reflectance based on the measurement result is about 46%, which substantially coincides with the minimum value obtained in the previous experiment. In the measurement results of this experiment, the optical thickness of the dye layer when irradiating the disk with an 8 mw laser beam that minimizes the reflectance of the disk was 260
It is presumed that it is near Å.

Next, under the same conditions as above, an experiment was conducted in which the thickness of the dye layer was set to 1600 ° and the change in the reflectivity of the disk corresponding to the change in the laser beam intensity was measured. Incidentally, the thickness (= 1600 °) at this time is expressed by the above equation (1).
6 is the film thickness of the recording layer calculated when m = 30. FIG. 6 shows the measurement results of such an experiment. In the same measurement results, the same characteristics as those in FIG. 3 are observed.

In this case, the minimum value of the reflectance is obtained when the intensity of the laser beam is 20 mw, and is 8 mw in the previous experiment.
This is because the thickness of the recording layer in this experiment is larger than the thickness of the recording layer in the previous experiment. It is estimated that the temperature did not rise.

From the above experiments, it is estimated that similar characteristics can be obtained even with the thickness of the recording layer determined at m = 32. However, as m increases, the heat capacity of the recording layer increases, and it is necessary to increase the laser power at the time of recording. Therefore, it is preferable to set the film thickness of the recording layer as small as possible.

The thickness of the dye layer is determined by the formulas (15) and (16).
D ₁ <d ≦ d ₂ using the thicknesses d ₁ and d ₂ determined by
It is good to set in the range. This is because, by setting in this way, the reflectance of the recording portion can be reduced by reducing the thickness of the dye layer during recording. However, there are cases where the thickness of the dye layer is further reduced than the minimum value of the thickness of the dye layer during recording to be set in the vicinity of d _1, in this case, the reflectivity of the recorded portion is higher than the reflectance of non-recorded portion Is also increased.
Thus, as also set the thickness of the dye layer in the range of d ₁ <d ≦ d _2, it is preferable to set as much as possible d ₂ vicinity. If the thickness of the dye layer is set to around d ₂ , the reflectance of the medium can be increased, which is also advantageous in this respect.

Further, the thickness of the recording portion of the dye layer is preferably set to around d _1. Therefore, the intensity of the laser beam at the time of recording is set so that the thickness of the recording portion becomes around d _1. Is better.

Next, an experiment in the case where the refractive index of the dye layer is set smaller than the above-mentioned refractive index will be described. In this experiment, the refractive index n ₁ of the dye layer was set to n ₁ = 2.0. Other conditions were the same as in the experiment of FIG. 4, and an experiment was performed to measure the reflectance of the disk when the thickness of the dye layer was changed. FIG. 7 shows the measurement results.

From the figure, it can be seen that even if the thickness of the dye layer is changed, a desirable maximum value and minimum value are not generated in the reflectivity of the disk.

The thickness of the dye layer used in this experiment was 500
Disk reflectivity was measured when the intensity of the laser beam was changed for three samples of {, 1000}, and 2100 °. FIG. 8 shows the measurement results. From the figure, it can be seen that, even if the laser power is changed between 0 and 15 mw for each sample, a decrease in reflectance cannot be obtained.

From the above, the dye material having a low refractive index as used in this experiment does not change the reflectance of the medium even if its thickness changes, so that the intensity of the reflected beam at the recording portion on the disk is not recorded. It can be confirmed that compared to the intensity of the reflected beam at the portion, the intensity cannot be changed significantly. Therefore,
The larger the refractive index of the dye used as the recording layer, the better.

Summarizing the above experiments, the larger the refractive index n ₁ of the dye material used as the recording layer, the better, and the thickness d of this dye layer is set in the range of d ₁ <d ≦ d _2. There is a need. At this time, in order to increase the reflectivity of the disk and to surely reduce the reflectivity of the recording portion relative to the reflectivity of the non-recording portion, it is preferable to set the thickness d near d ₂ . The thickness of the dye layer is preferably as thin as possible. The thickness of the dye layer of the recording portion is desirably set in the vicinity of d _1, it is preferable to set the laser beam intensity during recording in order to achieve this.

In the above embodiment, copper is used as the reflective layer, but other metals can be used. That is, if the imaginary component of the complex refractive index is sufficiently larger than the imaginary component of the complex refractive index of the dye, and the real component of the complex refractive index is sufficiently smaller than the real component of the complex refractive index of the dye, the metal contacts the dye layer. If it is made to do so, its reflectivity becomes high, so that it can be used. Such metals include copper, gold, silver and alloys thereof.

Needless to say, the recording medium having the structure used in the above embodiment can be used not only for disks but also for tapes and the like.

[0055]

According to the present invention, the recorded portion is reproduced during reproduction.
In addition, it is possible to provide an information recording method for an optical recording medium that can record information satisfactorily so as to have a low reflectance .

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of an existing write-once disc using an organic dye material as a recording layer.

FIG. 2 is a diagram showing a state where pits are formed on the same disk.

FIG. 3 is a graph showing a logical expression (12).

FIG. 4 is a view showing an experimental result.

FIG. 5 is a diagram showing experimental results.

FIG. 6 is a diagram showing experimental results.

FIG. 7 is a diagram showing experimental results.

FIG. 8 is a view showing an experimental result.

FIG. 9 is a diagram used to explain the principle of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Dye layer (recording layer) 3 Reflective layer 5 Depression (recording part)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigeo Yamamoto 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Minoru Kume 2-5-2 Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd. (72) Inventor Kotaro Matsuura 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) Reference E. Hamada et. al. "CD-compatible write-once with high frequency", SPIE Vol. 1078 Optical Data Storage Topical Meeting (Jan. Pages and Volume 2 Pages 294-296

Claims (2)

(57) [Claims] 1. A transparent substrate made of polycarbonate,
Recording laser beam on an optical recording medium comprising a light-transmitting recording layer formed on the transparent substrate, and a reflective layer formed on the recording layer and made of gold, silver, copper or an alloy thereof. To reduce the thickness of the recording portion of the recording layer
A method for recording information by reducing the reflectivity of the recording layer by Rukoto, the intensity of the recording laser beam, the thickness of the recording portion of the recording layer is set to be d _1, the the set recording laser beam and irradiating the optical recording medium, the optical recording medium information recording method. Where d ₁ is n ₀ , the refractive index of the transparent substrate is n ₀ , the real component of the complex refractive index of the recording layer, the imaginary component is n ₁ , k ₁ , the real component of the complex refractive index of the reflective layer, and the imaginary component is n ₂ , When k ₂ and the wavelength of the laser beam are λ, (M is an integer where d ₁ is positive and the reflectance at the interface between the transparent substrate and the recording layer is minimal at d ₁ ). Wherein in said formula defining the thickness d ₁ of the recorded portion of the recording layer, and sets the intensity of the laser beam so m is minimized claim 1
3. The information recording method for an optical recording medium according to item 1.